A "fun" solution to this_dude's problem in the #ruby irc channel: http://www.codewars.com/kata/sum-of-digits-slash-digital-root/train/ruby

this_dude.rb

class Proc
  def >> other
    -> arg { other.to_proc.call call arg }
  end
end

class Symbol
  def >> other
    to_proc >> other.to_proc
  end
end

class Enumerator
  class << self
    def generate value
      raise ArgumentError, 'No block given' unless block_given?

      Enumerator.new Float::INFINITY do |yielder|
        loop do
          yielder << value
          value = yield value
        end
      end
    end
  end
end

Enumerator.generate(942, &:digits >> :sum).find(&:digits >> :one?)
#=> 6